Independent school fees average around £12,000 a year for day pupils and £30,000 for boarders.
Photograph: Christopher Furlong/Getty Images

Independently-educated pupils receive a boost equivalent to two years of extra schooling over state school pupils even after adjusting for social and economic bias, according to new research.

The study by Durham University – the most sophisticated of its type to date – found that independent school pupils in England gained an advantage worth nearly two-thirds of a GCSE grade higher once the effects of income, gender and prior attainment were stripped out.

Privately educated elite continues to take top UK jobs, finds survey

Read more

“This difference equates to a gain of about two years’ normal progress and suggests that attending an independent school is associated with the equivalent of two additional years of schooling by the age of 16,” the research says.

Some critics of private schools have attributed their academic success to the advantages of wealth and background among families who can afford the fees, which average around £12,000 a year to attend as a day pupil and £30,000 for boarding.

The Durham research, funded by the Independent Schools Council, suggests that the attainment gap is larger than previously thought and can be found among all age groups, starting from the first years of primary school where pupils are aged four.

However, the researchers, led by Robert Coe, professor of education at Durham, confessed to being at a loss to explain exactly why private school pupils enjoyed such a large advantage in exam results.

“It is always difficult to unpick the causes of any differences – and we think it is unlikely to be purely an effect of better teaching in independent schools. But we find a clear and significant difference in the GCSEs achieved that is not explained by any of the factors we can account for,” said Coe.

The report said that “unobserved factors” could have affected the differences in GCSE results. “Due to these limitations the results must be interpreted with caution,” it noted.

William Richardson, former professor of education at Exeter and general secretary of the Headmasters and Headmistresses Conference of leading independent schools, said: “This is a particularly important piece of research which resets the dial on understanding how well pupils in England perform at different types of schools once background factors are taken into account.

Is it OK for politicians to send their children to private schools?

Read more

“The Durham researchers say they can’t explain the reason for the difference but the most obvious contender is the overall quality of teaching and learning, linked to a holistic education through which each child develops the confidence to do well.”

Rebecca Allen, director of the Education Datalab research group, said she thought the Durham findings were broadly accurate although it was difficult to gauge the full impact of private schooling.

“But even if sending a child to an independent school raises GCSE performance, this research doesn’t tell us whether it is worth the thousands of pounds a year parents would need to pay compared with cheaper options such as private tuition,” Allen said.

“Is this just telling us that families who spend a lot of money on private schools value education highly? I’m sure they have the social and economic capital to support their children in the home to a greater extent than many typical children at state schools.”

The Durham researchers estimated that if state schools improved their results to the level seen at independent schools, England would shoot up the league tables produced by the OECD’s programme for international student assessment (Pisa), putting the country ahead of European leaders such as Finland and on a par with Japan.

Richard Cairns, headmaster of Brighton College, was more downbeat about the results: “Frankly, this is not a cause for celebration for anyone. It is profoundly depressing to think that so many young people in England are underachieving through no fault of their own.

“I would urge the prime minister to put education back at the top of our political agenda. Ideally, we need a cross-party commission to consider where, as a country, we went wrong and how we can get ourselves back on track.”